1. Field of the Invention
The present invention relates to wind energy generators. More particularly, the present invention relates to the blade structure of wind generator apparatus. Additionally, the present invention relates to blades of the wind generator apparatus in which the blades are formed of dihedral sails.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
As fossil fuel supplies dwindle, renewable energy sources will be called upon more and more to produce power. One ubiquitous source of renewable energy is wind. Even a gentle breeze has substantial energy. Wind energy increases exponentially with wind velocity. Thus, a wind of eleven miles per hour has ⅓ more energy than a wind of ten miles per hour.
The class of devices which attempt to capture and utilize wind energy are known generally as wind motors or wind energy generators. The best known device of this class, the common windmill, has been used for centuries to derive mechanical energy from wind. The typical windmill has a set of blade-like vanes projecting radially from the end of a horizontal shaft. These vanes are elevated atop a supporting tower. The vanes and their associated horizontal shaft are free to rotate about a vertical axis so that a rudder-like arrangement can keep the vanes facing into the prevailing wind. The vanes are twisted in a manner which causes wind to impart a torque, and hence a rotational motion to them. The turning of the vanes turns the horizontal shaft which is typically geared to the vertical shaft which transmits the rotational energy to the ground level.
A contemporaneous version of the wind energy generator operates propellers or other suitable wind force collectors projecting radially in a horizontal plane from a vertically-disposed central shaft or support. Wind force collectors on the wind energy generator move with the wind for half a rotation and against the wind during the other half of the rotation. In order for wind to create a net force imbalance, wind force collectors must present more aerodynamic resistance while moving with the wind than while moving against the wind. It is well known to devise such wind force collectors by taking advantage of the fact that wind force collectors rotating in a horizontal plane present one profile while moving with the wind and the opposing profile while moving against the wind. Accordingly, wind force collectors have been provided with wind traps, shaped as cups or as hemispheres, whose open sides have high aerodynamic drag, face into the wind when moving with it and whose closed sides, having relatively low aerodynamic drag face the wind while moving against it.
One of the major problems associated with wind energy generators is the problem of wind drag loads on the blades. These loads severely limit the efficiency of the electrical generating system and they increase with increasing revolutions per minute of the blades. In the past, these undesirable effects of wind drag have been reduced by varying the blade pitch angle at the root of the blade, in a manner similar to aircraft propellers. This is accomplished through the use of complicated and expensive rotor hub assemblies which vary the pitch angle of the blade.
Blade designs operate on either the principal of drag or lift. For the drag design, the wind literally pushes the blades out of the way. Drag-powered wind turbines are characterized by slower rotational speed and high torque capabilities. The lift design of such wind turbines employs the same principle that enables airplanes, kites, and birds to fly. The blade is essentially an airfoil or wing. When the airflow passes the blade, a wind speed and pressure differential is created between the upper and lower blade surfaces. The pressure of the lower surface is greater and thus acts to “lift” the blade. The blades are attached to a central axis, such as in a wind turbine rotor, and the lift is translated into rotational motion. Lift-powered wind turbines have much higher rotational speed than drag types and therefore are better suited to electrical energy generation. Unfortunately, there are still strong drag effects which adversely affect the operation of such blade-type wind energy generators.
In the past, various patents have issued relating to wind turbines that utilize sail-type blades. U.S. Pat. No. 5,171,127, issued to Feldman, describes a vertical axis sail-bladed wind turbine. A plurality of flexible sail blades are attached to a vertically extending, rotatable shaft by upper and lower blade attachment devices. A power-absorbing leg device is coupled to the rotatable shaft. The flexible sail blades are deployed and stabilized in operation by the centrifugal forces produced in response to rotation of the blades about the vertical axis of the shaft. The sail blades are formed of elongate flexible sail panels. Flyweights are disposed between and secured to the ends of pairs of the sail panels. The blade is deployed so as to optimize energy capture. U.S. Pat. No. 5,183,386, issued to the same inventor, teaches that each of the sail panels is formed of a membrane of a woven or non-woven fabric, plastic or other material. A leading edge strength member, formed of a flexible cable of suitable material, is attached to the leading edge of the sail panel. The leading edge member is enclosed in a suitably-shaped aerodynamic fairing. The leading and trailing members take on the concave shape of the membrane edges to which they are attached. The curvatures of the leading edges of the panel will be correspondingly less than that of the trailing edges of the panels.
U.S. Pat. No. 4,049,362, issued to Rineer, describes another type of vertical axis wind-driven rotor assembly. This sails of this assembly are articulated to provide driving and feathering airfoil positions. The airfoils are triangular in shape with an apex extending downwardly. The degree of feathering action takes place as a result of wind pressure. This causes the panels to remain in an intermediate position between the extremes of articulation. The point of pivotal mounting of the airfoils is selected with regard to the center of the airfoil panel to assure that center of pressure is behind (with respect to the direction of rotation of the rotor) a line connecting the points of pivotal mounting of the air foil panels. As such, the configurations of the airfoils will be adjusted depending on the pressure exerted by the wind.
U.S. Pat. No. 6,402,472, issued to Hogue, teaches another type of sail-bladed windmill wheel in which the sails are mounted around a horizontally extending rotor. In high winds, a drawbar extension allows the angles of the blades to increase to a point where the area that the wind wheel presents to the wind is significantly reduced. The force of the wind behind the wheel is limited to a value that the wind wheel support surfaces can withstand. As the blade angle of the sail increases beyond the optimum, the sail becomes less and less efficient in capturing energy from the wind. As such, the sails will detach under those circumstances when excess wind is encountered by the sails.
It is an object of the present invention to provide a wind energy generator apparatus which minimizes the amount of drag affecting the blades.
It is another object of the present invention to provide a wind energy generator apparatus which maximizes the capture of wind and the force exerted by the wind on the blades.
It is another object of the present invention to provide a wind energy generator apparatus which minimizes the cost of the blade structure.
It is a further object of the present invention to provide a wind energy generator apparatus which facilitates the ability to recover energy from the apparatus and to facilitate the ability to repair and/or replace the generator mechanisms.
It is still another object of the present invention to provide a wind energy generator apparatus which maximizes the aerodynamic characteristics of the blades and the supporting structure.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.